Microscopes for carrying out eye operations are regularly used for operations in a front area of an eye. Should such interventions be undertaken in a rear area of an eye, it is necessary to supplement the microscope with a monitoring device, which makes it possible to focus on precisely this area of the eye. Such monitoring devices comprise at least one wide angle lens, or ophthalmoscopy lens, for wide-angle examination of the relevant rear part of the eye, wherein the ophthalmoscopy lens provides an intermediate image in a beam path in front of an objective lens of the microscope. This intermediate image cannot be focused with the microscope. Depending on the focal length of the auxiliary optics and of the examined eye, the intermediate image appears sharp in a position that lies closer to the object. To focus the intermediate image, it is necessary to shorten the focal length of the microscope object. A height adjustment of the microscope does not change the focal length. By using a reducing lens in the beam path beneath the microscope object, the plane of the intermediate image may lie in the focus of the microscope. In order to focus this intermediate image using the microscope, the microscope has to be moved or spaced in relation to the ophthalmoscopy lens over a distance. This change in height is basically determined by the individual refractive power of the eye, and by the different refractive power(s) of the selected ophthalmoscopy lens.
The two lenses are held by a positioning unit of the monitoring device, which is fixed directly on the microscope, and, if necessary, they can be positioned in the beam path without the need for considerable adjustment of the microscope during an operation. The positioning unit generally comprises a connection device, by means of which the positioning unit can be coupled to the microscope. The positioning unit is also formed in such a way that the relevant lens can be easily pivoted or slid into the beam path and removed therefrom again.
In order to adapt the intermediate image of the ophthalmoscopy lens, as precisely as possible, to a focal length of the microscope objective lens, at least one of the lenses is designed to be adjustable along the beam path of the microscope. In known monitoring devices, a linear guide is provided on the positioning unit, for example, for adjustment of the lens in a longitudinally displaceable manner, wherein the lens can be moved by means of an adjusting wheel having a screw drive. In order to prevent an accidental collision between the ophthalmoscopy lens and the eye, or to avoid possible damage to the eye during an operation, the positioning unit is formed in such a way that the ophthalmoscopy lens is movable, essentially without resistance, in the direction of the objective lens of the microscope, that is to say, it can move back in the event of a collision with the eye. For example, this is achieved by a second linear guide that also enables a longitudinal displacement of the ophthalmoscopy lens.
In addition to the above-described mechanical and optical requirements, it is important that the monitoring device and the positioning unit are basically sterile during an operation, so as to prevent a possible infection of an eye with germs, for example. In particular, there is a risk of infection since the monitoring device is advanced relatively tightly against the eye in question during an operation. The possibility of an infection of the patient's eye by an insufficiently prepared positioning unit is ruled out by use of a disposable positioning unit, supplied in a sterile state. It is therefore usual to sterilise the monitoring device and positioning unit in question before an operation, for example, by steam sterilisation. To carry out repeated sterilisation, it is absolutely necessary to form all components of the monitoring device and positioning unit, except for any seals made of resilient materials such as rubber, from metal or glass. Other materials, such as plastics materials, have not proven to be very durable for repeated sterilisation. The linear guides and the screw drive also have to be formed in a dimensionally accurate manner to ensure specific fits, and, therefore, only components made of metal are also considered in this instance. To prevent an infiltration of water into the guides during the sterilisation, these can be provided with rubber seals, or seals made of other resilient materials. It is also necessary to lubricate corresponding pairs of sliding surfaces of the guides, and of the screw drive, at regular intervals using a lubricant so as to ensure the function thereof.
The monitoring devices and positioning units known from the prior art pose a range of drawbacks. A weight of the monitoring device, which can be adapted, for example, to an adapter plate on the microscope screwed onto the microscope, is, therefore, relatively high and disruptive in the event of handling of the monitoring device during an operation. The linear guides can also only be sealed or sterilised with difficulty. During steam sterilisation, water or steam can only infiltrate the screw paths of the screw drive with difficulty, and, therefore, undesired water residues or germs may still remain in the screw paths after the steam sterilisation. It is also disruptive that the lubricants used are removed, at least in part, during the steam sterilisation and contaminate the water used for sterilisation. The sterilisation process itself is also to be considered problematic since it cannot be ruled out with absolute certainty that germs will still remain on the monitoring device and on the positioning unit after the steam sterilisation. The quality of a sterilisation process is, therefore, also dependent, inter alia, on water quality in a steam sterilisation apparatus.
Furthermore, a monitoring device and a positioning unit are to be sterilised after each use, and, therefore, the monitoring device and positioning unit cannot be used directly after use in subsequent eye operations owing to the sterilisation times. As the case may be, it is necessary to obtain and have available a plurality of monitoring devices and positioning units so that operations can be carried out without any time restraint. High overall costs for production, sterilisation, and maintenance of the monitoring device and positioning unit are thus sustained by a user, as well as costs incurred owing to increased capital investment.
The object of the present invention is, therefore, to propose a positioning unit and a monitoring device that comprises a movement mechanism that is easier to clean.